In a dot-matrix display system, such as an existing LCD screen, a frame is typically considered as a display unit. Each frame includes N display lines, and each display line includes M dots or pixels. When a controller of the display system updates a frame, it typically updates sequentially every display line from top to bottom. When each display line is updated, pixels are typically updated from left to right.
After a display line is updated and before the next display line is updated, there is a time interval called a horizontal blanking interval (HBI). Therefore, when a frame has N display lines, there will be N−1 HBIs when updating the whole frame. After the last pixel of a frame is updated and before updating of the next frame begins, there is a time interval called a vertical blanking interval (VBI). In this application, the term “a blanking interval” is used to collectively refer to both a HBI and a VBI.
In general, when a particular display line is updated, voltages of different levels are applied to all of the pixel electrodes on that display line, so as to cause different degree of light transmission on the liquid crystal of each pixel. Assuming touch driving and sensing electrodes are provided on the top surface of the LCD, mutual capacitive sensing can be used to sense any external conductive object. When updating a display line, said voltages may cause capacitive sensing effects on the touch sensing electrodes. As result, in the signals received by the touch sensing electrodes, there are not only driving signals emitted by the touch driving electrodes, but also noises arising from updating the display line. This is most severe when the touch driving electrodes are in parallel to the display lines, i.e. the touch sensing electrodes are perpendicular to the display lines.
One objective of the present application is to eliminate or alleviate electromagnetic interferences on the touch sensing electrodes during the updating of the display lines of the screen. Another objective of the present application is to allow a touch processor to be aware of the timing information for the BIs.